Conventionally known methods for producing coumarin and its derivatives include, for example, a process in which a 3-(2-cyclohexanoyl)propionic acid ester is heated in the presence of a hydrogenation-dehydrogenation catalyst, such as a palladium catalyst, thereby to allow the ester to undergo cyclization and dehydrogenation (as described in U.S. Pat. No. 3,442,910); and a process in which the cyclization and dehydrogenation reactions for producing coumarin and its derivatives are performed in the presence of both a noble metal catalyst such as a palladium catalyst and a promoter such as barium sulfate or nickel oxide (as described in JP-A-60-181082). (The term "JP-A" as used herein means an "unexamined published Japanese patent application.")
However, the conventional processes have been defective in that the yields of coumarin and its derivatives are not always high. In addition, there has been a problem that when the reaction is conducted under severe conditions in the initial stage thereof, the conversion of the 3-(2-cyclohexanoyl)propionic acid ester used as a starting material is low. If the reaction mixture resulting from the cyclization and dehydrogenation reactions contain the 3-(2-cyclohexanoyl)propionic acid ester, the ester comes into a final product to be obtained from the reaction mixture because removal thereof by purification is difficult, and the contaminant in the final product can be a cause of offensive odor.